1. Field of the Invention
The present invention relates to a waveguide type variable optical attenuator used widely in optical communications.
2. Description of the Related Art
Generally, in optical communications, there is widely used a waveguide type variable optical attenuator as an optical waveguide for attenuating light.
In prior art, a conventional waveguide type variable optical attenuator of this kind is shown in FIGS. 1A and 1B (See JP-A-2003-84252). This waveguide type variable optical attenuator 91 (the waveguide type optical component) comprises a Mach-Zehnder optical interference system formed using parallel input and output side Y-branch waveguides 92 and 93 arranged with a predetermined interval and 2 arm waveguides 94 and 95 for connecting these Y-branch waveguides 92 and 93; a heater 96 that serves as a phase shifter for heating one arm waveguide 94 of the arm waveguides 94 and 95 of this interference system, electrodes 97 and 98 formed for applying voltage to the heater 96, and a recessed groove 99 formed between the arm waveguides 94 and 95 so as not to transmit heater heat to the arm waveguide 95.
In such a waveguide type variable optical attenuator 91, when voltage is applied to the heater 96, the arm waveguide 94 is heated, so that the refractive index of the arm waveguide 94 is varied. Since this causes a difference in apparent optical path lengths of light propagated through both the arm waveguides 94 and 95, i.e., a variation in propagated light phases due to a thermal optical effect, the intensity of optical signals can be arbitrarily controlled by adjusting voltage applied to the heater 96.
As shown in FIG. 2, a conventional waveguide type variable optical attenuator (an optical switch) 100 has been proposed that comprises a waveguide 102 embedded in a substrate 101 excluding a portion, a heater 104 arranged on the substrate 101 via a buffer layer 103 to cover the waveguide 102, an insulation layer 105, and a heat dissipation projection 106 arranged in a region corresponding to the heater 104 (See JP-B-2687362).
In such a waveguide type variable optical attenuator, heat caused when the heater 104 is ON is forcedly dissipated from the heat dissipation projection 106 when the heater 104 is OFF, which can thereby result in an optical switching element that is capable of fast switching.
Use of such a waveguide type variable optical attenuator as an optical communication device requires considerably fast response time (10 msec or less).
In JP-A-2003-84252, however, because the heater 96 simply heats one arm waveguide 94 of the 2 arm waveguides 94 and 95, no desired response time can be obtained.
In JP-B-2687362, although heat caused by the heater 104 is dissipated from the heat dissipation projection 106 to thereby realize a fast optical switch, because the heater 104 simply heats the waveguide 102, no desired response time can be obtained similarly to the waveguide type variable optical attenuator shown in JP-A-2003-84252.